Connection errors - SMTP

From MozillaZine Knowledge Base

This article lists the error messages that you might see when you try to connect to an SMTP server to send mail. For each error message it identifies possible causes. For troubleshooting techniques, see: Cannot send mail

Some of these error messages are misleading. In particular, the "Please verify..." part of these messages is rarely helpful. The messages are long, making some of them look very similar. When you are troubleshooting, be careful to identify the error message exactly.

Sending mail to the SMTP server happens in stages. Different things can go wrong at each stage, so each stage has different error messages.

When a connection fails, Thunderbird provides you with up to four pieces of information about the failure. If you have to ask for support (for example, in a forum or from a helpdesk), ensure that you provide all the information:

The status message in Thunderbird's status bar and in the Sending Messages window. This tells you the stage that Thunderbird reached when the error occurred.

An error summary provided by Thunderbird. This is almost always: "Sending of message failed"

The detailed error message provided by Thunderbird. This is often misleading.

An embedded message from the server. Thunderbird includes this in its error message.

Note: If an error message shows the server name as "localhost", it usually means that you are using a webmail extension or an anti-virus program. In this case the error might be coming from that program, not from the SMTP server.

Thunderbird errors

Lookup

Thunderbird looks up the SMTP server's name to find its network address (IP address). The lookup service (DNS) is usually provided by your ISP as part of your Internet connection. The status message at this stage is "Looking up..."

An error occurred sending mail: Unable to connect to SMTP serverserver nameThe server may be down or may be incorrectly configured. Please verify that your Mail/News account settings are correct and try again.

The server does not exist (but it might exist when you are connected to some other network).

You typed the server name wrongly. (Even an extra space can make it fail.)

Connecting

Thunderbird connects to the SMTP server, and the SMTP server responds. The status message at this stage is "Connecting..."

The message could not be sent because connecting to SMTP serverserver namefailed. The server may be unavailable or is refusing SMTP connections. Please verify that your SMTP server setting is correct and try again, or else contact your network administrator.

or:

An error occurred sending mail: The mail server sent an incorrect greeting:message

You specified the wrong server. The server you specified exists, but it is not an SMTP server.

You specified the wrong port number. Ask whoever runs the SMTP server what the correct port number is.

The server is down. This is usually temporary. If it persists, contact whoever administers the server.

Your firewall is blocking the port.

Your ISP is blocking the port. This often affects port 25, and you can often work around it by using port 587, but details depend on your ISP and on the SMTP server's configuration.

In general, this indicates an error message was returned from the server, and that message is echoed as received.

If the error message is The server responded: Syntactically invalid EHLO argument(s), you may have encountered an issue caused by a faulty hostname used as argument for the initial greeting. This problem is frequently seen with Mac OSX. Following options:

make sure that the hostname of your machine does not have a dot (.), underscore (_), any other special character except hyphens (-), or line breaks in it (you will have to look up the respective operating-system setting);

if this doesn't work, or if you can't set the hostname on your machine, see this post for instructions on how to set the greeting argument explicitly (only characters, numbers, and hyphens "-" inbetween are allowed).

Security

If your settings require it, Thunderbird creates a secure connection using TLS or SSL. The status message at this stage is "Connected..."

The message could not be sent because connecting to SMTP serverserver namefailed. The server may be unavailable or is refusing SMTP connections. Please verify that your SMTP server setting is correct and try again, or else contact your network administrator.

You specified SSL, but the server does not support it. In this case Thunderbird makes a connection, but its attempt to use SSL times out, so the status message is "Connected...", and there is a delay (normally 60 seconds) before you see the error message.

Your anti-virus program doesn't support SSL.

See also the Logging in section, below.

An error occurred sending mail: Unable to connect to SMTP serverserver namevia STARTTLS since it doesn't support EHLO. Please verify that your Mail/News account settings are correct and try again.

Logging in

If your settings require it, Thunderbird logs in by sending your username and password. If the server does not accept the username and password combination, then Thunderbird asks you for the password again. If your password does not work, there might be various reasons:

You typed the wrong password. Perhaps it is case sensitive.

You specified the wrong user name. Perhaps it needs to be your entire e-mail address, or perhaps only part of your e-mail address.

You are connecting to the wrong server, and this server does not recognize your username.

Your user name is not yet registered on the server.

The server is broken.

The message could not be sent because connecting to SMTP serverserver namefailed. The server may be unavailable or is refusing SMTP connections. Please verify that your SMTP server setting is correct and try again, or else contact your network administrator.

You specified that a username and password are required, but you did not specify any username.

Network errors

Things can go wrong with the network at any stage in sending a message. These errors are not related to the SMTP server, but they can interrupt communication with the server, so that sending the message fails.

Server errors

Here is a list of the standard server error codes, and brief explanations. Servers often report different messages, they often represent the code with full stops, (like 4.2.1 instead of 421), and they often use non-standard codes (for example, 571 instead of 530).

Most of these errors usually indicate faults on the server. 530 or 551 means that you are using the wrong server name, or the wrong port, or you have not specified that Thunderbird must log in with your user name and password. 554 can mean that your ISP is blocking the port.